All topics
Ten in-depth topic pages, with an interactive BB84 simulator and calculators.
Quantum foundations for cryptography
The physics that makes quantum cryptography work: qubits, measurement, no-cloning, entanglement, Bell tests, entropy and the quant…
02 / TOPICClassical cryptography and the quantum threat
How RSA, Diffie–Hellman and elliptic curves work, why Shor’s algorithm breaks them, what Grover does to symmetric ciphers, and why…
03 / TOPICQuantum key distribution protocols
BB84, B92, six-state, SARG04, E91/BBM92, COW, DPS, continuous-variable, MDI, twin-field, device-independent and more, with worked …
04 / TOPICSecurity of QKD: attacks, proofs and post-processing
What “unconditional security” means, the assumptions behind it, decoy states, finite-key and composable security, error correction…
05 / TOPICPhotonic hardware: beam splitters, sources, detectors and channels
Beam-splitter quantum optics and the Hong–Ou–Mandel effect, photon sources, single-photon detectors, fibre and free-space channels…
06 / TOPICQKD networks: architectures, routing and deployments
Point-to-point links, trusted-relay and optical-switched networks, key management, physical-layer key-rate models, resource alloca…
07 / TOPICQuantum communication: teleportation, entanglement distribution and the quantum internet
Superdense coding, teleportation, entanglement swapping and purification, quantum repeaters and memories, the PLOB bound, free-spa…
08 / TOPICBeyond QKD: other quantum cryptographic tasks
Quantum random numbers, secret sharing, digital signatures, bit commitment and the no-go theorems, coin flipping, oblivious transf…
09 / TOPICPost-quantum cryptography and ML-DSA
Quantum-resistant classical cryptography: the NIST standards (ML-KEM, ML-DSA, SLH-DSA, FN-DSA, HQC), lattice mathematics, a detail…
10 / TOPICStandards, applications and outlook
Where quantum communication and cryptography are used, who standardises them, what the limits are and what to expect next.…
+ / PRACTICEWorked problems
Eleven problems with solutions.
+ / PRACTICEQuiz
Twelve questions with instant feedback.